How to Avoid Noise in Your Digital Photography

Digital "noise" is a common problem in digital cameras today. A lot of factors can introduce noise to your digital photography, but there are certain steps you can take to avoid it, as noise can obscure detail and removing it from your images can take precious time.

Digital noise usually represents itself as speckled pixels of colour in your images or as a grainy effect, and is generally considered undesirable. Read on to find out how to reduce the chances that your valuable images will be affected by digital noise.

Understand what a digital camera sensor is, and how it works. Unlike analog cameras, digital cameras work with a sensor instead of film. Sensors receive light and process it into electric charges via tiny photodiodes, whose outputs are reflected as pixels in your final digital image. These electrical charges tell the sensor what colour each corresponding pixel is meant to be and other information which will create the digital image.

 

Understand what digital "noise" is and what causes it. When light hits the sensor's photodiodes, a signal of electrons are produced in order to convey the light to the camera sensor. Electronic "noise" is the unwanted fluctuations in this signal. In a digital camera, noise manifests itself as speckles, usually colored and patternless. These are generally caused by unwanted electron flow in and around the sensor adding to the desired electron flow. Noise can be caused by imperfections in the sensor itself such as "hot pixels", randomness in the distribution of the limited numbers of photons available at low light levels, and the sensor or camera overheating.

 

Purchase higher-end, newer camera equipment. The most convenient, but expensive, way to combat noise is to buy a newer camera if yours is a few years old, with more expensive cameras being able to deliver better performance. Newer cameras have sensors that are developed to collect more light with less noise than those in older cameras, making them a good choice if you are struggling to control noise in your images and your gear is outdated.

• Choose a camera with a larger sensor. The problem with smaller sensors is that the light sensors are closer together than in a larger sensor, and that means the electrons overheating corrupt them faster due to their closer proximity. A larger sensor means that electrons will have to travel farther before corrupting their neighbouring light sensors. Full frame sensors are perfect for reducing noise in your images. A DSLR or large-sensor compact camera such as one in "Four Thirds" format is much better than a compact camera, even one a few years newer, although a full-frame DSLR is better still, as fast wide-angle and prime lenses for it are more widely available and cheaper.
• Pick a camera with fewer megapixels, or a lower resolution, in a given class. The more pixels there are on a camera's sensor, the closer they are together and the more likely overheating electrons will corrupt the light sensors. Although higher-end cameras generally have larger sensors with a high resolution or megapixel count, there are those which have larger sensors but still retain lower megapixel counts, making them perfect for dealing with digital noise.
• Pick a wide-aperture lens to maximize light intake. Some compact cameras have f/2.0 or f/2.8 lenses; a 50mm f/1.8 lens is inexpensive and excellent for a DSLR. These will allow the same shutter speed at one-half to one-quarter the ISO setting of a common f/3.5 or f/4.5 maximum aperture zoom lens (At the same f/ratio, the bigger camera is still better: it's collecting equally intense light into bigger photosites, for far more photons to process. The absolute size of the aperture for a given angle of view matters more). Lenses are a much more mature technology than cameras, so an interchangeable wide-aperture lens will improve your photography through many camera upgrades. Image stabilization allows faster shutter speeds but tends not to be built into wide aperture lenses, making those better overall as they stop subject motion too; a fast lens and compatible in-body image stabilization is a great combination.

Switch your camera's exposure to manual mode and adjust the settings which may introduce noise. When the camera is on automatic, or in program mode, as is the case with most lower-end cameras of the "point-and-click variety", your images are more likely to have noise as the camera changes the exposure by itself, and quite often it will introduce factors that introduce noise to your images. Taking control of your camera and exposure settings will help you eliminate factors which could contribute to digital noise in your photographs. Your camera's instruction manual will contain all instructions on how to adjust the various settings on your camera.

• It's OK to use a semi-automated exposure mode, but be sure to manually set a low ISO if possible. For instance, you could use aperture-priority mode with a wide aperture, which will allow a relatively short shutter speed with any given ISO. You could use your camera's exposure-compensation or bracketing function to try different exposures near the one the camera thinks is right.
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  Reduce your ISO. ISO is the setting which controls how light sensitive your camera's sensor is. A lower ISO (for example ISO 200) means your sensor is less sensitive to light, but is also less likely to create digital noise, while a higher ISO (for example ISO 400, or ISO 800) makes your camera sensor more sensitive to available light, but also increases the chance your images will have noise. Check your camera's manual on how to adjust the ISO setting.
  • If you need a higher ISO for a correct exposure with a fast-enough shutter speed to avoid blur from a lack of camera support or moving subject, use it. Adding a few speckles of high-ISO noise is better than smearing the picture with blur or wiping out its shadow detail with underexposure.
• Use a faster shutter speed, or rather, avoid long exposures. Long shutter speeds (for example, exposures of 5 seconds, or 30 seconds or longer) create more noise as they make the camera's sensor overheat faster. Faster shutter speeds give less chance for the sensor to overheat. So consider adding more light to your image to reduce the exposure time, and reduce the chance of noise: turn on some lamps, or use a flash. If you can't add more light, or it would spoil the picture (like one of lights outdoors at night), a slightly slower shutter speed and a lower ISO will provide the best results, as described below.
• Increase your signal-to-noise ratio with a low ISO and generous exposure. If you let a lot of light into your camera, preferably quickly, it will overpower the noise and give you an acceptable image. Use a low ISO setting, which amplifies the sensor's signals relatively little, and exposure to go with it (Some kinds of noise can accumulate over time, and even accrue more rapidly as the sensor warms through use, but a longer exposure is still generally better than a higher ISO). The lowest setting is usually best, but you'll usually have to look for noise to notice it up to ISO 400 with a compact camera or old DSLR, and up to ISO 1600 with a modern (2011) DSLR.

Turn the camera's noise reduction setting on, if it has one. This feature is usually found in higher-end cameras. In-camera noise reduction is usually helpful in combating noise in your images, especially those of a longer exposure or in low light conditions. However be aware, it does smooth the fine detail in your images, making them softer to the eye, which can be problematic, so only use this setting if you feel that noise will a serious problem while shooting. PC software can often smooth noise in post production, while preserving detail better than that supplied in the camera's internal computer, and you can revert to your original image if you decide you didn't want so much smoothing, or even any at all.

• You can use "dark frame subtraction" – making a preliminary or subsequent "exposure" of the same length as the actual exposure but with the lens capped to detect noise to delete from the final image to compensate for "hot pixel" and other camera imperfection noise. Some cameras can do it automatically, not bothering to open the shutter for the dark exposure, but you can perform it yourself, even with a compact camera. This technique does not smooth your image, so is a suitable option for those who are worried about other noise reduction methods.

Make your image as bright as possible. It may seem obvious, but the less shadow there is in your image, the less chance noise will have together there. Noise generally appears in darker areas of your images (where there's less light to overpower it), so whether you introduce a new light source, such as a lamp or flash, move to a better-lit area, change your exposure settings to allow more light or photograph lighter subjects, reducing the amount of shadow in your image will reduce the amount of noise.

• Night pictures can be tricky because the highlights are actually the light sources. Like the sun during the day, they're much brighter than the surrounding areas which receive and reflect back to the camera only a little of their light. A camera's light meter averaging their brightness with their surroundings as if they were ordinary highlights will underexpose them for one big, noisy over-dark shadow. Try increasing the exposure significantly over what it suggests.
• Very bright lights can cause streaking or "bloom" with the CCD sensors usually found in cheaper cameras. Try to avoid having them close-by in the image.

Avoid using digital zoom, such as those frequently found on lower-end cameras or "point-and-click" varieties. Digital zoom is technically not zooming at all; it is in fact cropping and enlarging from a small area of the sensor. It should especially be avoided when that small area is clouded by noise.

 

Keep your camera stored in a cool place before you use it. The cause of most noise is a thermal reaction. The warmer your camera is, the more likely the sensor will overheat in a shorter period of time. Making sure your camera is cool, especially when in hot conditions, can greatly improve your camera's performance and reduce the likelihood of digital noise. Excessive heat such as that in uninsulated areas of a car in the sun, will be harmful for cameras regardless.

 

Take further steps to combat noise in post production, such as the aforementioned "dark frame subtraction" or noise reduction software. Sometimes, no matter what actions you take to reduce noise, it may still occur in your photos. In these cases you should take the time to learn and implement noise reduction in post processing.